I would assume that it falls under the broad umbrella of unsportsmanlike conduct, just as if he spit on him or gave him a cheap shot, but I can't say that I have seen anything like that happen.

two words for the receiver though...

DOUBLE TIE!

It pays to be prepared. I can see it now... it's the SB and the Pats need a TD to seal the game. Welker gets the ball and only Kurt Coleman stands between him and daylight. Coleman dives for his ankle and pulls off Welker's shoe, only to discover...